In a metal oxide semiconductor field-effect transistor (MOSFET) that is used as a switch circuit of a relay, a large induced current is input to the drain since the drain is connected to an external power supply via a coiled wire. In order to protect the MOSFET from this induced current, a technique of connecting a diode between the drain and the gate of the MOSFET for clamping a voltage is proposed. However, if the clamp voltage of the diode is high, the MOSFET cannot be protected effectively and if the clamp voltage is low, the diode itself may be damaged.